In orthopaedic surgery, bones are often fused together to prevent pain, improve function, and heal injuries. In settings of impaired blood supply, massive bone loss, or complicated trauma, techniques such as bone grafting or implanting metal are used to facilitate fusion or reconstruction. However, bone grafts have limitations of strength and available amounts of donor bone. Metal implants are also imperfect because if they are not securely fixed in living bone, they go onto fatigue and failure. In addition, both bone grafting or implanting can be problematic when there is inadequate blood supply to the repaired region including the bone or implant. Insufficient blood supply increases the risk of infection and limits the amount of bone formation in and at the interface of the implant with the bone (osteogenesis).
Some have tried vascularized bone grafting where blood is supplied by veins or conduits naturally forming part of the bone graft. This technique uses natural/actual bone with an attached blood vessel where the bone is harvested from the patient or donor, and then the harvested bone is used to fuse or reconstruct bones. It is known that the increased blood supply speeds healing, reduces infection, and increases strength. Unfortunately, however, current vascularized bone grafts must be harvested from the patient, increasing morbidity, lengthening recovery time, and increasing surgical complexity, such as infection risk. In addition, the number, size and shape of current vascularized bone grafts are limited. Lastly, these grafts are not usually taken from another animal or person due to immunologic graft-rejection issues.
As can be seen, there is a need for a system that combines the strength of a metal implant with a more effective blood supply than the supply provided by native vascularized bone implant or graft. It may be desirable to minimize large avascular regions in a bone graft or implant which can harbor bacteria. It also may be desirable to avoid the risk and disadvantages which currently exist with a massive bone harvest with later use of the bone harvest as a bone graft or implant. Even further, even if a bone harvest could be readily used without regard to problems associated with the act of harvesting bone, there is a need and advantages to providing an implant that can be made in a plurality of shapes and sizes that would not be available or at least readily obtained from a harvest of natural bone from a patient.
The advantages of a vascularized porous metal implant device include (1) the device not being limited by size or shape as compared to naturally harvested bone, (2) there is not a breakdown of the metal implant, (3) the device promotes bone growth into the core of the implant across a fusion gap between two pieces of bone being fused or connected and (4) the device lowers infection rate of implant by increasing blood circulation throughout the implant. These and other advantages will become apparent from the discussion set forth below.